NASA has released this image of Pluto, the final and best full-frame image taken by New Horizons as it speeded towards its encounter with the dwarf planet. Visible is the light-coloured area informally dubbed ‘the heart’. Credit: NASA.

NASA’s New Horizons spacecraft is due to make its closest approach to Pluto at 9:49:57pm Australian Eastern Standard Time tonight (Tuesday, 14 July 2015).

At that time, the craft will be busy taking numerous images and other data of the icy world and its retinue of moons, so it won’t be simultaneously beaming back signals. Those signals will have to wait until after the encounter, when the data will slowly be returned to Earth.

Nevertheless, there will be great excitement at mission control, and you’ll be able to follow it all through NASA’s live coverage online.

NASA TV will be broadcasting special coverage beginning at 9:30pm AEST.

]]>Hubble to search for worlds beyond Plutohttp://spaceinfo.com.au/2014/06/17/hubble-to-search-for-worlds-beyond-pluto/
Tue, 17 Jun 2014 09:57:02 +0000http://spaceinfo.com.au/?p=7868NASA’S NEW HORIZONS spacecraft, launched in January 2006, is closing in on its primary target, the dwarf planet Pluto. Arrival at the icy outer world is on track for 14 July 2015.

But when it reaches Pluto, New Horizons won’t be able to stop and admire the scenery. By necessity (ie. orbital mechanics and the fact that it doesn’t have a rocket motor to slow itself down) it will go sailing straight past, after having given us our first-ever close up glimpse of what used to be called the ninth planet. (I still do call it the ninth planet. Ed.)

This was always the plan. And the plan also calls for a second stage for the mission – a visit to one or more other icy worlds that orbit the Sun far beyond Pluto.

Artist’s impression of the New Horizons spacecraft at Pluto.

They’re called Kuiper Belt objects (KBOs), as they belong to a family of small, ice bodies that live in that part of the Solar System, called the Kuiper Belt.

The aim is to redirect New Horizons – once it has passed Pluto – onto a course that will take it near one or more of these KBOs.

But even though astronomers have been hunting for candidate KBOs for some years, they’ve yet to find one that is in the right place for New Horizons to visit. Yet there are probably some there that they just can’t see at the moment. So they’ve put out a call for help from the telescope best suited to spot any hidden KBOs – the Hubble Space Telescope.

This week, the Hubble Space Telescope Time Allocation Committee – the body that decides who gets to use the telescope – has recommended it be pressed into service.

The telescope will examine a small region of space to see if it can spot any KBOs. The first step will be doing a pilot study to see if Hubble can indeed spot KBOs in that region and at that distance – 8 billion kilometres from the Sun.

If it finds any, that will give the astronomers enough confidence to push ahead with a deeper, longer search to find the candidate KBOs for New Horizons to visit.

This image, taken by NASA’s Hubble Space Telescope, shows five moons orbiting the distant, icy dwarf planet Pluto. The green circle marks the unnamed moon, designated P5, as photographed by Hubble’s Wide Field Camera 3 on July 7 2012. The unnamed moon P4 was uncovered in Hubble imagery in 2011.

THE DISCOVERER OF PLUTO’S two tiniest moons are inviting the public to help select names for the new moons. By tradition, the moons of Pluto have names associated with Hades and the underworld.

“The Greeks were great storytellers, and they have given us a colourful cast of characters to work with,” said Mark Showalter, Senior Research Scientist at the Carl Sagan Centre of the SETI Institute in Mountain View, California.

Pluto has five moons – Charon (discovered 1978), Nix and Hydra (discovered 2005), and two known simply as P4 and P5, discovered in 2011 and 2012 respectively. Astronomers are now looking for names for P4 and P5.

Moons of the underworld

All the bodies in the Pluto system are named after mythological figures of the underworld – Pluto, the god of the underworld; Charon, the ferryman of the dead; Nix, Greek goddess of darkness and night; and Hydra, the nine-headed serpent that battled Hercules.

Showalter and the teams of astronomers who made the discoveries will select two names based on the outcome of the voting. Like Pluto’s three other moons, Charon, Nix and Hydra, they need to be assigned names derived from Greek or Roman mythology.

Artist’s impression of the New Horizons spacecraft passing Pluto in 2015.

Visitors to the website will also be able to submit their own suggestions. These will be reviewed by the team and could be added to the ballot. Voting will end February 25, 2013. The final names will be announced after their formal approval by the International Astronomical Union.

First mission to Pluto

P4 was discovered in 2011 in images taken by the Hubble Space Telescope. P5 was discovered a year later during a more intensive search for previously unseen objects orbiting the distant, dwarf planet. The moons are only 20 to 30 kilometres across.

Currently, Pluto is receiving special scrutiny by astronomers, because NASA’s New Horizons spacecraft is slated to arrive there in July 2015.

Launched in 2006, the craft is carrying some of the ashes of the man who discovered Pluto in 1930, Clyde Tombaugh.

A Google+ Hangout is scheduled on February 11 at 11:00am US PST (19:00 GMT) with two of the scientists involved in the discovery. Mark Showalter is from the SETI Institute, and Hal Weaver is a researcher at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.

Questions from viewers will be taken during the event using Twitter hashtag #PlutoRocks, the SETI Institute Facebook page and the Google hangout.

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If an alien civilisation builds brightly-lit cities, like those shown in this artist's conception, future generations of telescopes might allow us to detect them. This would offer a new method of searching for extraterrestrial intelligence elsewhere in our Galaxy.

IN THE SEARCH FOR EXTRATERRESTRIAL INTELLIGENCE, astronomers have hunted for radio signals and ultra-short laser pulses. But in a new proposal, Avi Loeb (Harvard-Smithsonian Centre for Astrophysics) and Edwin Turner (Princeton University) suggest a new technique for finding aliens—look for their city lights.

“Looking for alien cities would be a long shot, but wouldn’t require extra resources. And if we succeed, it would change our perception of our place in the universe,” said Loeb.

As with other SETI methods, they rely on the assumption that aliens would use Earth-like technologies. This is reasonable because any intelligent life that evolved in the light from its nearest star is likely to have artificial illumination that switches on during the hours of darkness.

Telling night from day

How easy would it be to spot a city on a distant planet? Clearly, this light will have to be distinguished from the glare from the parent star. Loeb and Turner suggest looking at the change in light from an exoplanet as it moves around its star.

As the planet orbits, it goes through phases similar to those of the Moon. When it’s in a dark phase, more artificial light from the night side would be visible from Earth than reflected light from the dayside. So the total flux from a planet with city lightingwill vary in a way that is measurably different from a planet that has no artificial lights.

Current technology could spot city lights on Pluto (artist's impression).

Spotting this tiny signal would require future generations of telescopes. However, the technique could be tested closer to home, using bodies at the edge of our Solar System.

Closer to home?

Loeb and Turner calculate that today’s best telescopes ought to be able to see the light generated by a Tokyo-sized metropolis at the distance of the Kuiper Belt—the region occupied by Pluto, Eris, and thousands of smaller icy bodies. So if there are any cities out there, we ought to be able to see them now.

By looking, astronomers can hone the technique and be ready to apply it when the first Earth-sized worlds are found around distant stars in our galaxy.

“It’s very unlikely that there are alien cities on the edge of our Solar System, but the principle of science is to find a method to check,” Turner said. “Before Galileo, it was conventional wisdom that heavier objects fall faster than light objects, but he tested the belief and found they actually fall at the same rate.”

As our technology has moved from radio and TV broadcasts to cable and fibre optics, we have become less detectable to aliens. If the same is true of extraterrestrial civilisations, then artificial lights might be the best way to spot them from afar.

Adapted from information issued by Harvard-Smithsonian Centre for Astrophysics. Images by David A. Aguilar (CfA) and ESO.

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ASTRONOMERS USING THE Hubble Space Telescope have discovered a fourth moon orbiting the icy dwarf planet Pluto. The tiny, new satellite, temporarily designated P4, was uncovered in a Hubble survey searching for rings around the dwarf planet.

The new moon is the smallest discovered circling Pluto. It has an estimated diameter of 13 to 34 km. By comparison, Charon, Pluto’s largest moon, is 1,043 km across, and the other moons, Nix and Hydra, are in the range of 32 to 113 km in diameter.

“I find it remarkable that Hubble’s cameras enabled us to see such a tiny object so clearly from a distance of more than 5 billion km,” said Mark Showalter of the SETI Institute, who led this observing programme with Hubble.

This composite of two Hubble images—taken on June 28, 2011 and July 3, 2011—shows Pluto's four satellites in motion. P4 is the as-yet-unnamed new moon.

Mission to Pluto

The finding is a result of ongoing work to support NASA’s New Horizons mission, scheduled to fly through the Pluto system in 2015. The mission is designed to provide new insights about worlds at the edge of our Solar System.

Hubble’s mapping of Pluto’s surface and discovery of its satellites have been invaluable to planning for New Horizons’ close encounter.

“This is a fantastic discovery,” said New Horizons’ principal investigator Alan Stern of the Southwest Research Institute. “Now that we know there’s another moon in the Pluto system, we can plan close-up observations of it during our flyby.”

Moons formed in a smash-up

The new moon is located between the orbits of Nix and Hydra, which Hubble discovered in 2005. Charon was discovered in 1978 at the US Naval Observatory and first resolved using Hubble in 1990 as a separate body from Pluto.

The dwarf planet’s entire moon system is believed to have formed by a collision between Pluto and another planet-sized body early in the history of the Solar System. The smash-up flung material that coalesced into the family of satellites observed around Pluto.

An artist's concept of Pluto's satellite system with newly discovered moon P4 highlighted.

Lunar rocks returned to Earth from the Apollo missions led to the theory that our moon was the result of a similar collision between Earth and a Mars-sized body 4.4 billion years ago.

Scientists believe material blasted off Pluto’s moons by micrometeoroid impacts may form rings around the dwarf planet, but the Hubble photographs have not detected any so far.

No sign of rings yet

“This surprising observation is a powerful reminder of Hubble’s ability as a general purpose astronomical observatory to make astounding, unintended discoveries,” said Jon Morse, astrophysics division director at NASA Headquarters in Washington.

P4 was first seen in a photo taken with Hubble’s Wide Field Camera 3 on June 28. It was confirmed in subsequent Hubble pictures taken on July 3 and July 18. The moon was not seen in earlier Hubble images because the exposure times were shorter.

There is a chance it appeared as a very faint smudge in 2006 images, but was overlooked because it was obscured.

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An artist's impression of Pluto and its largest moon, Charon. Astronomers have detected thin traces of carbon monoxide gas in the dwarf planet's atmosphere.

ASTRONOMERS HAVE DISCOVERED carbon monoxide in the atmosphere of Pluto, capping off nearly two decades of work to detect the gas in the ‘air’ of the distant, icy world.

Pluto, discovered in 1930, was long considered the Sun’s smallest and most distant planet. Since 2006, though, it has been regarded by many astronomers as a ‘dwarf planet’…one of a handful of such bodies with sizes of hundreds of kilometres that orbit in the distant reaches of the Solar System, out beyond Neptune.

Pluto is the only dwarf planet known to have an atmosphere. The thin layer of gases was detected in 1988 when it dimmed the light of a distant star as Pluto passed in front of it.

The new results, obtained using the 15-metre James Clerk Maxwell Telescope in Hawaii, show a strong signal of carbon monoxide gas.

Team leader Dr Jane Greaves of the University of St Andrews will present the new discovery today at the UK National Astronomy Meeting in Wales.

Fragile atmosphere

Previously, Pluto’s atmosphere was known to be over a hundred kilometres thick, but the new data raise this height to more than 3,000 kilometres—a quarter of the way out to Pluto’s largest moon, Charon.

In 1989 Pluto made its closest approach to the Sun, a comparatively recent event given that it takes 248 years to complete each orbit. The gases probably result from solar heating of surface ice, which sublimates (goes directly from ice to gas) as a consequence of the slightly higher temperatures during this period.

The resulting atmosphere is probably the most fragile in the Solar System, with the top layers blowing away into space.

“The height to which we see the carbon monoxide agrees well with models of how the solar wind strips Pluto’s atmosphere,” commented team member Dr Christiane Helling, also of the University of St Andrews.

Artist's impression of the view from the surface of Pluto, showing a thin, hazy atmosphere.

Deep space cold snap

The gas is extremely cold, about -220 degrees Celsius. A big surprise for the team was that the CO measurement was more than twice as strong as an upper limit obtained by another group, who used the IRAM 30-metre telescope in Spain in 2000.

“It was thrilling to see the signal gradually emerge as we added in many nights of data”, said Dr Jane Greaves, the team leader from the University of St Andrews.

“The change in brightness over the last decade is startling,” she added. “We think the atmosphere may have grown in size, or the carbon monoxide abundance may have been boosted.”

Such changes have been seen with Pluto before, but only in the lower atmosphere, where methane—the only other gas ever positively identified—has also been seen to vary.

Critical balance

Unlike the greenhouse gas carbon dioxide, carbon monoxide acts as a coolant, while methane absorbs sunlight and so produces heating. The balance between the two gases—which are just trace elements in what is thought to be a nitrogen-dominated atmosphere—is critical for its fate during the many-decades long seasons.

The newly discovered carbon monoxide may hold the key to slowing the loss of Pluto’s atmosphere. But if the chilling effect is too great, it could result in nitrogen snowfalls and all the gases freezing back onto the ground.

“Seeing such an example of extra-terrestrial climate-change is fascinating”, says Dr Greaves. “This cold, simple atmosphere that is strongly driven by the heat from the Sun could give us important clues to how some of the basic physics works, and act as a contrasting test-bed to help us better understand the Earth’s atmosphere.”

The JCMT is operated jointly by the UK, Canada and the Netherlands and is approaching its twenty-fifth anniversary.

The team has another Pluto observing run scheduled at the JCMT for the end of April, and in the long-term, they hope to continue tracking the changes in the atmosphere at least up to the fly-by of NASA’s New Horizons space probe in 2015.

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This artist's conception shows the dwarf planet Haumea, which is in the Kuiper Belt beyond Neptune. Pan-STARRS is expected to find hundreds of new Kuiper Belt Objects.

IN THE OUTER REACHES of our Solar System lies a mysterious region far more remote and difficult to explore than the Australian outback. It remains the only part of our Solar System not visited by spacecraft.

Called the Kuiper Belt, this area beyond Neptune is home to the dwarf planets Pluto, Eris, Makemake, and Haumea. It also harbours thousands of smaller objects that form a second, icy asteroid belt (or more appropriately, comet belt).

A new Earth-based telescope has begun to study this region, and already is scoring discoveries.

The Panoramic Survey Telescope & Rapid Response System (Pan-STARRS) PS1 telescope has found ten Kuiper Belt residents. Based on their brightnesses, the newfound objects range in size from 300 to 500 kilometres.

“We’re excited that Pan-STARRS is beginning to find these objects,” said Smithsonian astronomer Matthew Holman, who leads the Pan-STARRS-1 Outer Solar System Key Project.

“It marks the tip of the iceberg for future Pan-STARRS discoveries,” he added.

10 million times fainter

Pan-STARRS PS1 Observatory just before sunrise on Haleakala, Maui.

The Outer Solar System Key Project is part of a larger survey to which 60 percent of Pan-STARRS telescope time will be devoted. PS1 became fully operational in June 2010.

Over the course of the coming months and years, PS1 will repeatedly survey the full sky that is visible from its location on Haleakala, spotting objects as faint as magnitude 23 (10 million times fainter than visible to the unaided eye).

“By the end of the survey, we’ll have an essentially complete census of everything brighter than the survey’s limiting magnitude,” said Holman. This corresponds to Kuiper Belt Objects about 180 miles in diameter or larger.

Pan-STARRS will enable planetary astronomers to locate many new Kuiper Belt Objects and characterise their orbits. This will provide a firmer understanding of the structure, dynamics, and evolution of bodies in the outer Solar System.

Pan-STARRS is also likely to be a productive tool for discovering new comets.

Pan-STARRS-1 is a 1.8-metre-diameter telescope featuring the world’s largest digital camera—a 1.4-gigapixel monster that can photograph an area of the sky as large as 36 full moons in a single exposure.

Adapted from information issued by CfA. Images by CfA and Rob Ratkowski.

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New Horizons image of the planet Neptune. Its largest moon, Triton, can be seen be seen just off to one side. The spacecraft was almost 3.5 billion kilometres away from the pair when it took this image!

New Horizons spots Neptune and its moon Triton

Triton orbits Neptune the “wrong way”

Triton is often considered to be a twin of Pluto

NASA’s Pluto-bound New Horizons spacecraft—now a little over halfway there—has turned its attention to the planet Neptune and its largest moon, Triton.

Mission controllers periodically test the spacecraft’s cameras by aiming them at other Solar System bodies.

New Horizons’ Long Range Reconnaissance Imager (LORRI) snapped several images of Neptune during the latest annual systems checkout, which ended July 30. Neptune was 23.2 astronomical units (about 3.48 billion kilometres!) from New Horizons when LORRI took aim at the gas giant planet—and Triton made a cameo appearance.

Because Neptune and Triton were so far away, they are hard to tell apart in the images. But Triton can be seen as a dot or blob just off to one side.

New Horizons spacecraft prior to launch in 2006.

“That we were able to see Triton so close to Neptune, which is approximately 100 times brighter, shows us that the camera is working exactly as designed,” says New Horizons Project Scientist Hal Weaver, of the Johns Hopkins Applied Physics Laboratory. “This was a good test for LORRI.”

“As New Horizons has travelled outward across the Solar System, we’ve been using our imagers to make just such special-purpose studies of the giant planets and their moons because this is a small but completely unique contribution that New Horizons can make—because of our position out among the giant planets,” says New Horizons Principal Investigator Alan Stern, of the Southwest Research Institute.

Pluto’s twin: an enigma

Triton was discovered on October 10, 1846 by English astronomer William Lassell, just 17 days after Neptune itself had been discovered (by German astronomer Johann Gottfried Galle).

Dark streaks show where Triton's ice geysers have been active.

Neptune’s big moon is very unusual, in that it is the only large moon that goes around its planet backwards. That is, Neptune rotates from west to east (as does Earth), but Triton orbits in the planet from east to west (unlike our Moon). This is called a retrograde orbit.

The only plausible explanation is that Triton’s didn’t form along with Neptune, but rather was captured as it wandered past. Given that it is almost a twin of Pluto, it is supposed by most astronomers that Triton was a member of the Kuiper Belt—the swarm of small icy worlds that orbit the Sun beyond Neptune.

Triton also is quite big—its diameter of 2,700 kilometres makes it the seventh largest moon in the Solar System.

Its surface is a frozen crust of mostly nitrogen, underneath which is a core thought to be composed of rock and metals and making up two-thirds the moon’s mass.

One of the amazing things about Triton is that it has active geological features. When NASA’s Voyager 2 probe flew past in 1989, it spotted dark geysers shooting up from the surface, and dark streaks on the surface downwind of the geysers. The only other Solar System bodies confirmed to have volcanic activity are Earth, Jupiter’s moon Io, and Saturn’s moon Enceladus.

Unlike many moons—which are covered in craters—Triton has few impact craters. Scientists put this down to the geological activity, such as tectonic processes and volcanoes, which can reshape the landscape and wipe out any traces of craters. But unlike the volcanoes on Earth, on this frozen world the lava consists of water and ammonia!

Voyager 2 also sensed a thin atmosphere as it went past—observations made from Earth in 1990s indicated that the atmosphere was, at that time, thicker than when Voyager was there.

Pluto, here we come!

New Horizons was launched on January 19, 2006, on a trajectory and with a velocity that to reach Pluto in the minimum possible time. In consequence, New Horizons is the fastest spacecraft to leave Earth, having reached a velocity of 58,536 km/h after launch.

The spacecraft reached the orbit of Jupiter in February 2007, passed the orbit of Saturn in June 2008, and is not far away from the orbital distance of Uranus.

New Horizons is due to reach Pluto on July 14, 2015, and conduct a fly-by. It is not equipped with a rocket system to slow down and go into orbit around Pluto; instead, it will go sailing past.

But for around 200 days leading up to the encounter, it will start taking images that are better than best images we currently have of the icy world, so there will be plenty of time to make new discoveries.

Following the encounter, New Horizons will continue into deep space. There is a strong chance that mission controllers will be able to target the spacecraft to do a subsequent fly-by of one of the other icy worlds that inhabit the Kuiper Belt.

Adapted from information issued by NASA / JHU APL.

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A New Horizons spacecraft Long Range Reconnaissance Imager (LORRI) image of Jupiter and two of its moons, taken on June 24 when the spacecraft was 2.4 billion kilometres from the giant planet.

New Horizons spacecraft bound for Pluto

Has taken images of Jupiter and Neptune

Pluto rendezvous set for July 14, 2015

NASA’s Pluto-bound spacecraft, New Horizons—which in December 2009 passed the halfway mark in its 10-year journey to the distant world—has turned around to take a look back into the middle part of the Solar System.

On June 24, the spacecraft’s Long Range Reconnaissance Imager (LORRI) was trained on Jupiter, the largest planet in the Solar System.

Artist's impression of how the New Horizons spacecraft will look during its fly-by of Pluto in July 2015.

A little over three years ago, New Horizons made a close fly-by of Jupiter to pick up speed using a “gravitational slingshot”. Now, in July 2010, the spacecraft is 2.4 billion kilometres from the planet—1,000 times further than it was at the moment of closest approach during that fly-by.

“The picture is a dramatic reminder of just how far New Horizons, moving about a million miles [1.6 million kilometres] a day, has travelled,” says mission Principal Investigator Alan Stern, of the Southwest Research Institute.

Despite the huge distance, the disc of Jupiter is readily apparent due to the planet’s large size. And because from LORRI’s perspective there was a good angle between Jupiter and the Sun, the planet looks a bit like a half full Moon.

And speaking of moons, two of Jupiter’s can faintly be seen—Ganymede on the left and Europa on the right.

Calibration image

The main aim of the Jupiter image was to test LORRI’s susceptibility to sunlight. LORRI is designed to operate in the distant, pitch black environment of Pluto, where sunlight is hundreds of times dimmer than it is here on Earth. So the camera is very sensitive; too much light would damage it. Which is why the Jupiter image was made with an exposure of only 0.009 second, and why the two moons appear so faint.

“We wanted to see how much stray sunlight would creep into these Jupiter pictures, especially since we’ll make observations of the Pluto system in a similar geometry after the spacecraft passes Pluto in 2015,” says Project Scientist Hal Weaver, of the Johns Hopkins University Applied Physics Laboratory.

“We generally prefer to look at targets in the opposite direction from the Sun. In fact, LORRI is calibrated for the low light we’ll see in the Pluto system and Kuiper belt. Pointing too close to the Sun could damage the camera, but we decided it was safe to try to observe Jupiter.”

“The observations were successfully executed and the images look great.”

Neptune as seen by New Horizons from a distance of around 3.4 billion kilometres.

A glance at Neptune

LORRI also was pointed toward another of the Solar System’s planets, Neptune. The huge blue world is around six times further from the Sun than Jupiter, so in the LORRI image it looks just like a fuzzy star.

The 100-millisecond exposure, made on June 23 when New Horizons was still 23 astronomical units from Neptune (one astronomical unit is the distance between the Sun and the Earth), was part of a navigation system test. New Horizons is equipped with “optical navigation”, a fancy term that means trajectory corrections during the final stages of its approach to Pluto will be aided by taking pictures of the planet and comparing its apparent position with its calculated position.

Even though no detail can be made out on Neptune’s disc, scientists can still use the images to learn more about the planet’s atmosphere, by seeing how sunlight scatters off the molecules.

On course for Pluto

At the beginning of July, the New Horizons team instructed the spacecraft to make a 35.6-second burn of its thruster. Calculations had shown the craft drifting slightly off course, due to a tiny amount of force applied by heat coming from the spacecraft’s radioisotope power source and reflecting off the main antenna!

With the burn correctly executed, New Horizons is on target for its closest approach to Pluto at 7:49am US EDT on July 14, 2005.

Due to mass constraints, the craft is not equipped with a braking rocket, so it will not be able to stop. Instead, it will go sailing straight past the tiny dwarf planet at a great rate of knots, and then head out into deep space. Mission planners are hoping they can find one or more candidate Kuiper Belt Objects—the small, icy worlds that inhabit the outer Solar System—and steer New Horizons to another rendezvous.

Our very best views of Pluto's surface, made from multiple Hubble Space Telescope images taken in 2002-03. From 200 days out, New Horizons will begin to take better photos than these.

Even though New Horizons will be unable to stop at Pluto, that doesn’t mean it won’t get a good look at the small planet and its three known moons. From roughly 200 days before the encounter right through until many days after, the spacecraft will take images that are better than the Hubble Space Telescope can produce.

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